The U.N. secretary-general is launching an internal audit of the interaction between the world body and two organizations that U.S. prosecutors have accused of bribing a former top U.N. official.

Ban Ki-moon's spokesman, Stephane Dujarric, said Thursday that the Office of Internal Oversight would review contact between the Global Sustainability Foundation and the Sun Kian Ip Group and the use of any funds received from them.

"This is a sign of the secretary-general's concern about the serious nature of the allegations," Dujarric said.

The two organizations are alleged to have been part of a multiyear bribery scheme to promote the interests of Chinese businessman Ng Lap Seng, also known as David Ng. Ng, 67, runs the Macau-based Sun Kian Ip Group.

On Tuesday, U.S. authorities arrested John Ashe, 61, at his home in a New York suburb. In 2013, Ashe was president of the 68th session of the U.N. General Assembly. Before that, he was Antigua and Barbuda's U.N. ambassador for nearly a decade.

Authorities said that starting in 2011, Ashe accepted over $1 million in bribes and committed tax fraud in support of billionaire Ng. Authorities have charged Ashe, Ng and four others in the scheme, including Francis Lorenzo, 48, the Dominican Republic's deputy U.N. ambassador.

Conference center

In a 37-page complaint, prosecutors said Ng was seeking Ashe's influence to promote the building of a multibillion-dollar U.N. conference center in Macau. They allegedly funneled money to Ashe through at least two nongovernmental organizations. While not named in the complaint, the organizations match the description of South-South News and the Global Sustainability Foundation. Lorenzo is president of South-South and Ashe is honorary chairman of the Global Sustainability Foundation.

"John Ashe, the 68th president of the U.N. General Assembly, sold himself and the global institution he led," U.S. Attorney Preet Bahara said Tuesday in announcing the arrest.

He said Ashe allegedly used the money to fund a lavish lifestyle that included at least one luxury trip for him and his family, Rolex watches, custom-made suits and a $30,000 basketball court at his home.

On Tuesday, a judge set Ashe's bail at $1 million and ordered the former diplomat to wear an electronic monitoring bracelet. The U.S. attorney's office said Thursday that Ashe had not posted bail and remained in custody.

If convicted, he could face at least six years in prison.

A bail hearing has been set for Friday morning for Lorenzo, the Dominican diplomat. He is charged with multiple bribery-related charges that carry potential penalties of up to 15 years in jail.

Ng and another of his associates were arrested in mid-September on separate charges.

U.N. shocked

Dujarric told reporters Tuesday that the U.S. attorney's office did not inform the secretariat of the investigation, nor did the U.N. chief ever discuss Ng's hoped-for Macau conference center with Ashe.

"I think all of this was news to us when we read about it in the paper this morning," he said. Dujarric added that the secretary-general was "shocked and deeply troubled" by the allegations, which he said "go to the heart of the integrity of the United Nations."

The U.S. attorney said the investigation was continuing.

"I'm not commenting on who may be in cross hairs, who may be arrested," Bharara told reporters this week. "It's early and we're looking at a lot of things, and I wouldn't be surprised if you would see other people charged."